Preparation of primary alkyl esters



United States Patent 3,474,131 PREPARATION OF PRIMARY ALKYL ESTERS Louis Schmerling, Riverside, Ill., assignor to Universal Oil Products Company, Des Plaines, 111., a corporation of Delaware No Drawing. Filed Oct. 31, 1966, Ser. No. 590,542 Int. Cl. C07c 67/04, 69/ 76, 69/22 U.S. 'Cl. 260-497 13 Claims ABSTRACT OF THE DISCLOSURE Primary alkyl esters are prepared by treating a carboxylic acid with an olefin in the presence of an acidic catalyst, such as alkanesulfonic acid, at a temperature above about 200 C.

This invention relates to a process for preparing primary alkyl esters. More particularly, the invention is concerned with a process for esterifying carboxylic acids and unsaturated hydrocarbons in the presence of certain compositions of matter whereby primary alkyl esters will be obtained.

Esters of carboxylic acids and particularly primary alkyl esters will find a wide variety of uses in the chemical field especially in those fields where a primary alkyl ester is desired, due to the specific physical behavior of primary esters as opposed to secondary esters. The primary alkyl esters will find use as intermediates in the preparation of plastics, resins, pharmaceuticals, waxes, etc. In addition, if the ester contains a long-chain alkyl and is normal in configuration, the ester may be subjected to hydrolysis. Upon hydrolysis the ester will yield primary alcohols which, in the case of long-chain alcohols, make excellent alkylating agents for use in the preparation of biodegradable detergents. In addition, the lower esters of carboxylic acids containing a primary alkyl portion may also be used as a fragrance, said esters possessing fruit-like or flowerlike aromas.

It is therefore an object of this invention to provide a process for preparing primary alkyl esters of carboxylic acids.

A further object of this invention is to provide a process for esterifying carboxylic acids with an unsaturated hydrocarbon in the presence of certain compositions of matter to prepare primary alkyl esters of carboxylic acids.

In one aspect, an embodiment of this invention resides in a process for obtaining primary alkyl esters which comprises treating a carboxylic acid with a l-alkene in the presence of an acidic catalyst at a temperature above about 200 C., and recovering the resultant primary alkyl ester.

A specific embodiment of this invention is found in a process for obtaining a primary alkyl ester which comprises treating acetic acid with l-pentene in the presence of methanesulfonic acid at a temperature in the range of from about 225 C. to about 250 C. and recovering the resultant n-pentyl acetate.

Other objects and embodiments will be found in the following further detailed description of this invention.

As hereinbefore set forth, the present invention is concerned with a process for preparing primary alkyl esters of carboxylic acids utilizing certain compositions of matter as catalysts, the particular types of catalyst being hereinafter set forth in greater detail, at elevated temperatures.

Suitable carboxylic acid which may be esterified utilizing the catalysts of the present invention comprises monocarboxylic acids containing from 2 to about 20 carbon atoms or more. The preferred acids are saturated in nature and will include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthylic acid, caprylic acid, pelargonic acid, capric acid, undecylic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, nondecylic acid, aracidic acid, etc.; or aromatic acids such as benzoic acid, toluic acid, etc. It is also contemplated within the scope of this invention that dibasic acids such as succinic and phthalic acid or unsaturated acids such as oleic acid may also be esterified with an unsaturated compound utilizing the same compositions of matter as catalysts, although not necessarily with equivalent results.

The esterification agents which are used in the process of this invention to form the desired product comprises unsaturated hydrocarbons and particularly alkenes. These olefins will include straight-chain hydrocarbons and branched-chain hydrocarbons as well as aromatic hydrocarbons which contain an unsaturated side chain. The olefins which are used to prepare the primary alkyl ester will contain from 2 to about 22 carbon atoms or more and will preferably contain a carbon atom chain containing from 8 to 16 carbon atoms. The preferred olefins will comprise alpha-olefins such as ethylene, propylene, l-butene, 1- pentene, 2-methyl-l-butene, l-hexene, 2-methyl-1-pentene, the isomeric alpha-heptenes, octenes, nonenes, decenes, undecenes, dodecenes, tridecenes, tetradecenes, pentadecenes, hexadecenes, heptadecenes, octadecenes, nondecenes, eicosenes, heneicosenes, docosenes, etc.; styrene, alpha-mthylstyrene, allylbenzene, etc. Olefins which yield alpha-olefins under the reaction conditions are also utilizable.

The esterification of the aforementioned carboxylic acids with an unsaturated hydrocarbon is effected in the presence of certain catalytic compositions of matter. As hereinbefore set forth, it has been found that certain compositions of matter will catalyze the addition of carboxylic acids to an olefinic hydrocarbon. The compositions of matter which will find use as novel catalysts in this reaction comprises acidic substances such as mineral acids and certain metal halides (i.e., protonic acid catalysts and Lewis acid catalysts). The protonic acid catalysts include sulfuric acid, phosphoric acid, alkanesulfonic acids, arylalkane-sulfonic acids, etc. The Lewis acid catalysts include zinc chloride, boron fluoride, addition complexes such as boron fluoride-ethyl etherate, etc, In general, use of catalysts such as sulfuric acid or aluminum chloride causes much polymerization and other side reactions at the elevated temperatures used in the process of this invention. This will, of course, result in a lower yield of the desired product. For this reason, preferred catalysts of this invention comprised alkanesulfonic acids and mild Friedel-Crafts metal halide catalysts. Preferred alkanesulfonic acids include those in which the alkyl portion of the radical will contain from 1 to about 6 carbon atoms or more. Examples of these alkanesulfonic acids which find use as catalysts will include methanesulfonic acid, ethanesulfonic acid, l-propanesulfonic acid, 2-propanesulfonic acid, l-butanesulfonic acid, Z-butanesulf-onic acid, 2-methyl-2-propanesulfonic acid, the isomeric pentane-, hexane-, etc., sulfonic acids.

The relative yield of primary alkyl esters to secondary or tertiary alkyl esters may be increased by the added presence of an organic peroxide or oxygen (for example, in the form of air). The esterification of the carboxylic acid with the olefinic hydrocarbon will be elfected at esterification conditions which will promote the obtention of primary esters, the esterification conditions being mainly concerned with the temperature at which the reaction is etfected. It has now been discovered that when temperatures above about 200 C. and preferably in a range of from about 225 to about 250 C. are used, a primary ester will be obtained. In addition, it is also contemplated that a relatively wide range of pressures may also be used, said pressures ranging from atmospheric up to about 50 atmospheres or more. When utilizing a gaseous olefin as an esterification agent, a superatmospheric pressure may be obtained by charging the desired amount of gaseous olefin to the reaction vessel. In addition, the gaseous olefin may be used to effect only a partial pressure at which the reaction is effected, the remainder of the pressure being provided for by the introduction of an inert gas such as nitrogen into the reaction vessel. In general, the pressure need only be that needed to keep the reactants in contact with the catalyst at the temperature of the reaction.

The process of this invention may be effected in any suitable manner and may comprise either a batch or continuous type operation. For example, when a batch type operation is used, a quantity of the particular carboxylic acid which is to be esterified and the olefinic hydrocarbon are placed in an appropriate apparatus such as, for example, a rotating autoclave which contains the particular catalyst which is to be used. The autoclave is sealed and heated to the desired operating temperature which as hereinbefore set forth, is in excess of about 200 C., and maintained thereat for a predetermined residence time which may range from about 0.25 to about hours or more. In addition, if so desired, super-atmospheric pressures may be utilized using the manner which has hereinbefore been set forth in greater detail. Upon completion of the desired residence time, the reaction apparatus and contents thereof are allowed to cool to room temperature and the reaction mixture is recovered. The reaction mixture is then subjected to separation by any means well known in the art such as fractional distillation or crystallization, chromatography, etc., whereby the desired ester is separated from any isomeric ester, by-products, unreacted starting materials and the catalyst.

It is also contemplated within the scope of this invention that the esterification of the carboxylic acid with an esterifying agent such as an olefinic hydrocarbon in the presence of an acidic catalyst at the desired reaction temperature to prepare primary esters may be effected in a continuous manner of operation. When a continuous type of operation is used, the starting materials comprising the particular carboxylic acid and the olefinic hydrocarbon are continuously charged to an appropriate reaction vessel which is maintained at the proper operation conditions of temperature and pressure. If the catalyst is a solid (for example, phosphoric acid impregnated on kieselguhr) it may be kept in the reaction vessel. If it is a liquid (for example an alkanesulfonic acid), it may be charged through a separate line, or if so desired, it may be admixed with one of the aforesaid starting materials, particularly the carboxylic acid, prior to entry into said vessel and the mixture thereafter charged thereto in a single stream. Upon completion of the desired residence time, the reactor efiluent is continuously withdrawn from the reactor and subjected to a separation whereby the desired primary alkyl ester is separated from any unreacted starting materials, by-products, and catalyst. The unreacted starting materials and catalyst may be thereafter recycled to form a portion of the feed stock, while the desired ester is recovered and removed to storage.

The following examples are given to illustrate the process of the present invention, which, however are not intended to limit the generally broad scope of the present invention in strict accordance therewith.

EXAMPLE I In this example, 50 g. of propylene and 102 g. of propionic acid along with 6 g. of methanesulfonic acid and 1 g. of di-t-butyl peroxide Were placed in the glass liner of a rotating autoclave. The autoclave was sealed and an initial pressure of atmospheres of nitrogen was charged. The autoclave and contents thereof were rotated at a temperature of 250 C. for a period of 8 hours. During this time, the maximum pressure rose to 100 atmospheres. At the end of the 17 hours, the autoclave and contents thereof were cooled to room temperature, the excess pressure was vented and the reaction mixture recovered. The

desired product comprising n-propyl propionate was recovered.

EXAMPLE II In this example, 50 g. of propylene, 102 g. of propionic acid and 6 g. of methanesulfonic acid were placed in the glass liner of a rotating autoclave. The autoclave was sealed and a pressure of 30 atmospheres was reached by charging 10 atmospheres of air and 20 atmospheres of nitrogen. The autoclave was then heated to a temperature of 225 C. and maintained thereat for a period of 8 hours. During this time, the maximum pressure rose to 82 atmospheres. Upon completion of the desired residence time, the heating was discontinued and the autoclave allowed to return to room temperature, the pressure being 30 atmospheres. This excess pressure was vented and the reaction product recovered. The desired product comprising n-propyl propionate was recovered from the reaction mixtures; its yield was, lower than that obtained in Example I.

EXAMPLE III In this example, 50 g. of l-pentene and g. of propionic acid along with 6 g. of methanesulfonic acid was treated in a manner similar to that hereinbefore set forth; that is, the mixture was placed in the glass liner or a rotating autoclave which was thereafter sealed. Sufiicient nitrogen was charged so that an initial pressure of 30 atmospheres was reached. The autoclave was heated to a temperature of 225 C. and maintained thereat for a period of 8 hours, during which the maximum pressure rose to 78 atmospheres. At the end of the 8 hours, the autoclave and contents thereof were cooled to room temperature, the final pressure at room temperature being 30 atmospheres. The excess pressure was vented and the reaction product removed. The desired product comprising n-pentyl propionate was recovered.

EXAMPLE IV In this example, 59 g. of propylene and 100 g. of caproic acid along with 5 g. of methanesulfonic acid were placed in the glass liner of a rotating autoclave. The autoclave was sealed and an initial pressure of 30 atmospheres was reached by charging in 15 atmospheres of air and 15 atmospheres of nitrogen. The autoclave was heated to a temperature of 225 C. for a period of 8 hours. During this time, the maximum pressure at the operating temperature reached 81 atmospheres. The autoclave and contents thereof were allowed to cool to room temperature and the pressure being 28 atmospheres. The excess pressure was vented and the reaction product removed from the autoclave. The desired ester comprising n-propyl caproate was recovered.

EXAMPLE V A mixture of 50 g. of propylene, 51 g. of caproic acid and 6 g. of a boron fluoride etherate catalyst was placed in the glass liner of a rotating autoclave. The liner was sealed and 30 atmospheres of nitrogen was pressed in. The autoclave was then rotated at a temperature of 225 C. for a period of 4 hours. During this time, the maximum pressure in the autoclave rose to 88 atmospheres. At the end of the 4 hours, the autoclave and contents thereof were allowed to cool to room temperature, the final pressure at room temperature being 30 atmospheres. The excess pressure was vented and the reaction mixture was recovered from the autoclave. The desired product comprising n-propyl caproate was recovered.

EXAMPLE VI A mixture of 50 g. propylene, 50 g. of caproic acid and 5 g. of zinc chloride were treated in a manner similar to that set forth in Example V above, that is, the mixture was placed in an autoclave, an initial pressure of 30 atmospheres of nitrogen was pressed in and the autoclave was rotated at a temperature of 225 C. The autoclave was maintained at this temperature for a period of 8 hours, during which time the maximum pressure rose to 96 atmospheres. After cooling the room temperature, the autoclave was opened after the final room temperature of 30 atmospheres had been vented and the reaction mixture was recovered. The desired product comprising n-propyl caproate was separated and recovered.

EXAMPLE VII A mixture of 70 g. of benzoic acid, 50 g. of propylene and 8 g. of methanesulfonic acid was placed in the glass liner of a rotating autoclave. The autoclave was sealed and an initial pressure of 30 atmospheres of nitrogen was vented thereto. The autoclave and contents thereof were rotated at a temperature of 225 C. for a period of 8 hours. During this time, the maximum pressure in the autoclave rose to 67 atmospheres. At the end of the 8 hour period, the autoclave and contents thereof were allowed to cool to room temperature, the final pressure at room temperature being 30 atmospheres. Following this, the excess pressure was vented and the autoclave opened. The reaction mixture was removed and subjected to separation. There was recovered a 50% yield of propyl benzoate, 12% of this yield being n-propyl benzoate.

I claim as my invention:

1. A process for obtaining primary alkyl esters which comprises treating a saturated aliphatic or aromatic hydrocarbon monocarboxylic acid containing from 2 to about 20 carbon atoms with an alpha-mono-olefinic hydrocarbon containing from 3 to about 22 carbon atoms in the presence of an alkane sulfonic acid catalyst at a temperature above about 200 C., and recovering the resultant primary alkyl ester.

2. The process as set forth in claim 1, further characterized in that said carboxylic acid is acetic acid.

3. The process as set forth in claim 1, further characterized in that said carboxylic acid is propionic acid.

4. The process as set forth in claim 1, further characterized in that said carboxylic acid is caproic acid.

5. The process as set forth in claim 1, further char- 6 acterized in that said mono-olefinic hydrocarbon is propene.

6. The process as set forth in claim 1, further characterized in that said mono-olefinic hydrocarbon is lpentenc.

7. The process as set forth in claim 1, further characterized in that said catalyst is methanesulfonic acid.

8. The process as set forth in claim 1, further characterized in that said catalyst is ethanesulfonic acid.

9. The process as set forth in claim 1, further characterized in that said catalyst is propanesulfonic acid.

10. The process as set forth in claim 1, further characterized in that the esterification is carried out at a temperature in the range of from 225 to 250 C.

11. The process as set forth in claim 1, further char- .acterized in that said primary alkyl ester is n-propyl acetate.

12. The process as set forth in claim 1, further characterized in that said primary alkyl ester is n-pentyl propionate.

13. The process as set forth in claim 1. further char- .acterized in that said primary alkyl ester is n-propyl caproate.

References Cited JAMES A. PATTEN, Primary Examiner V. GARNER, Assistant Examiner U.S. C1. X.R. 

